<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<script src="../js/jquery-3.4.1.min.js"></script>
		<script>
			$(function(){
				///$("#f li:first").css({"border":"4px solid red","background-color":"yellow"});
				//$("#f li:last").css({"border":"15px solid blue","background-color":"yellow"});
				$("#f li").first().css({"border":"4px solid red","background-color":"yellow"}).end().last().css({"border":"30px solid blue","background-color":"yellow"});
			});
		</script>
	</head>
	<body>
		<ul id="f">
			<li>桃子</li>
			<li>香蕉</li>
			<li>梨子</li>
			<li>菠萝</li>
			<li>萝卜</li>
		</ul>
		<input type="button" name="s" id="b1" value="改变首尾的样式" />
	</body>
</html>
